Inductor for Heating Ultraheavy Oil and Oil Sand Deposits

ABSTRACT

The invention relates to a plug element ( 10 ), in particular for producing capacitors (C), which comprises three sections ( 1, 2, 3 ) in the direction of its longitudinal extent, wherein a first section ( 1 ) has a tapered shape at one end of the plug element ( 10 ), said tapered shape complementing a shape of a third section ( 3 ) at that end of the plug element ( 10 ) which is averted from the first section ( 1 ), and wherein a second section ( 2 ) is arranged between the first and the third section ( 1, 3 ), said second section connecting the first and the third section ( 1, 3 ) to one another. The invention also relates to a plug system ( 100 ) comprising plug elements ( 10 ) by means of which (cylindrical) capacitors (C) can be created, wherein electrically conductive layers (L 1 , D, L 2 , U) of the capacitor (C) which is formed from the plug system ( 100 ) simultaneously form a conduction structure of an inductor.

The invention relates to a plug element and also to a plug system that can be plugged together therewith, in particular for producing cylinder capacitors.

In order to convey extra-heavy oils or bitumen from oil sand or oil shale reserves by means of pipe systems, which are introduced into said deposits by drilling, the flowability of the oils has to be considerably increased. This can be achieved by increasing the temperature of the reserve (reservoir), for example by means of a steam assisted gravity drainage (SAGD) method.

In the case of the SAGD method, steam, to which solvent can be added, is pressed under high pressure through a pipe running horizontally within the reservoir. The heated, molten bitumen separated from the sand or rock seeps to a second pipe, placed approximately 5 m deeper, through which the liquefied bitumen is conveyed. Here, the steam has to perform a number of tasks simultaneously, specifically to produce the introduction of the heat energy for liquefaction, the separation from sand and also the pressure build-up in the reservoir, on the one hand in order to make the reservoir geomechanically permeable for bitumen transport (permeability) and on the other hand in order to enable the bitumen to be conveyed without additional pumps.

In addition to the SAGD method or instead of this method, an inductive heater can be used in order to assist or convey extra-heavy oils or bitumen.

Here, the electromagnetically inductive heater consists of a conductor loop, which is placed in the reservoir and, when energized, induces Eddy currents in the surrounding earth, which heat said earth. In order to achieve the desired heat output densities of typically 1-10 kW per meter of inductor length, it is necessary, depending on the conductivity of the reservoir, to apply amperages of several hundreds of amps at frequencies of typically 20-100 kHz. For compensation of an inductive voltage drop along the conductor loop, capacitors are interposed, whereby a series resonant circuit is produced, which is operated at the resonance frequency thereof and constitutes a purely ohmic load at the terminals. Without these series capacitors, the inductive voltage drop of the conductor loops, which are up to a few hundred meters long, would add up from tens of kV to more than 100 kV at the connection terminals, which can hardly be managed inter alia in respect of the insulation with respect to the earth. Furthermore, there would have to be a compensation of the reactive power at or in the generator (oscillator).

The problem of capacitively compensated inductors with plastic-based insulation or dielectric systems lies in the upwardly limited operating temperature range. The voltage and partial discharge resistance reduces considerably when temperatures of approximately 150° C. are reached or exceeded. Whereas in the case of heavy oil reservoirs a temperature increase of up to 50° C. for example may be sufficient to considerably accelerate the conveyance, in the case of bitumen (oil sand) reservoirs higher temperatures (>100° C.) are generally necessary. In the case of hybrid methods (SAGD assisted by inductive heating, or EM-SAGD), it must additionally be expected that steam from an injector or a swelling steam chamber reaches the inductor, such that temperatures above 200° C. may be present at the inductor. These may result in voltage breakdowns or partial discharges.

Capacitively compensated inductors with concentrated, ceramic-based capacitors for increased temperature resistance for inductive heating of heavy oil and oil sand deposits is an inductor having mechanically rigid concentrated capacitors, which are connected by flexible externally insulated pipes, are already known. The necessary temperature resistance is to be achieved by the use of ceramic-based capacitors. The same demand, however, on the electrical insulation properties is also placed on the external insulation of the pipes. Since, however, the external insulation does not simultaneously have the function of a dielectric, the layer thickness can be increased. However, the demand with regard to temperature resistance and flexibility remains.

In addition, distributed capacitors based on coaxial line structures are known. Here, resonance lengths around 10 m or greater and capacitor portions with 1-2 m length are formed. To this end, a separate external insulation is necessary.

Proceeding from the prior art, the object of the invention is to create a device of suitable design for electrically or electromagnetically heating a reservoir of an oil sand deposit.

This object is achieved by means of a plug element, which in the direction of longitudinal extent thereof comprises three portions, wherein a first portion at one end of the plug element has a tapered shape, which is complementary to a shape of a third portion at the end of the plug element remote from the first portion, and wherein a second portion is arranged between the first and the third portion and interconnects the first and the third portion. By means of the plug element, individual components can be built modularly when a plurality of identical plug elements are joined together. In anticipation of the following embodiments, electrical components, for example capacitors of variable physical size and capacitance, can be “plugged together” here in a particularly advantageous manner.

In an advantageous embodiment, the plug element in the direction of longitudinal extent thereof has a through-opening from the end of the first portion to the end, remote therefrom, of the third portion. “Hollow” components, for example pipes, can thus be produced in a simple manner.

It is particularly expedient if the plug element is rotationally symmetrical. In this way, shapes and components can be produced with which identical physical properties can be impressed, for example in the radial direction, as is necessary with many components.

In accordance with this purpose, individual portions of the plug element have a plurality of layers of different material type arranged coaxially with one another, which differ in portions in terms of number.

In a further advantageous embodiment, the coaxially arranged layers of the first portion and the coaxially arranged layers of the third portion supplement one another to form the respective layers of the second portion arranged coaxially with one another (in layer sequence and thickness of the selected material). By way of example, cylindrical capacitors, depending on the arrangement and material selection of the coaxial layers, can thus be plugged together to form a “large” component.

With a suitable embodiment of the plug element, radial bores can be provided in the second portion of the plug element. Since the second portion is generally thicker in terms of the “wall” thickness thereof compared with the two other portions of the plug element, it is also mechanically more stable. The second portion, also referred to as the middle portion, is thus suitable for receiving bores or recesses thereon.

In a further advantageous embodiment, radial grooves are provided in the second portion of the plug element and can be filled with a certain material, for example with a plastic. The grooves can be provided inside or outside the cross section of said second portion. Due to a selective “weakening” of the radial cross section, the mechanical properties of the plug element can be varied, for example. The plug element is more resilient in the second portion due to the provided grooves. The grooves additionally can be filled with plastic, whereby a possible freedom of movement can be limited.

A further aspect of the invention concerns a plug system formed from a plurality of plug elements, in which at least two plug elements can be plugged together to form a plug system, in that in each case a first portion of a plug element can be plugged into a third portion of a further plug element, and so on. Depending on requirements, components of variable size and properties can thus be “plugged together”.

Such plug elements, which can be plugged together to form a capacitor of variable size and capacitance, wherein the individual layers arranged coaxially with one another of the plug system formed by means of the plug elements comprise at least two layers of electrically conductive material, between each of which a layer of dielectric material is arranged, are particularly suitable. Capacitors of almost any “size” can thus be produced, in particular those that are suitable for a compensation of inductances that occur at amperages of a few hundred A at frequencies of approximately 20-100 kHz, for example as in the above-described method for heating oil reservoirs.

Lastly, when designing capacitively compensated inductors with plastic insulation systems, the considerably reduced voltage and partial discharge resistance at higher temperatures has to be taken into consideration. This can be implemented by considerably reducing the voltages occurring across the capacitors. To this end, it is necessary to increase the number of capacitors connected in series in such a way that the total inductive voltage drop is distributed between so many capacitors that the voltage limit reduced on account of the increased temperature is observed. The series connection of more capacitors, however, reduces the overall capacitance, which is to be compensated by increased capacitance of the individual capacitor when the operating frequency (=resonance frequency) is to be held constant.

In the case of distributed capacitors, which utilize the capacitance between conductor groups, this leads to an increased cross section of the line with accordingly increased material use. Furthermore, the number of interruptions due to reduced resonance lengths increases, which is associated with further increased production outlay.

In a further particularly advantageous embodiment of the invention, a plurality of plug elements, which can be plugged together to form a capacitor of variable size and capacitance, simultaneously form a line structure of an inductor. A universal concept for producing an electric or electromagnetic heater of a reservoir of an oil sand deposit can thus be created.

Further details and advantages of the invention will emerge from the following description of figures illustrating exemplary embodiments, in which:

FIG. 1 shows a structure of a plug element in accordance with one embodiment of the invention on the basis of a section parallel to the axis of rotation;

FIG. 2 shows the structure or assembly of a plug system by means of plug elements in accordance with the embodiment from FIG. 1 on the basis of a section parallel to the axis of rotation;

FIG. 3 shows a perspective view of a section parallel to the axis of rotation of a plug element in accordance with a further embodiment of the invention;

FIG. 4 shows a structure of a plug element in accordance with a further embodiment of the invention on the basis of a section parallel to the axis of rotation.

Identical or identically functioning units are provided in the figures with like or corresponding reference signs.

FIG. 1, in a sectional view symmetrical with respect to the axis of rotation, illustrates the structure of a plug element 10 in accordance with one embodiment of the invention. The plug element 10 is a plug element 10 by means of which a cylinder capacitor C “can be plugged together”. Here, the plug element 10 is divided into three portions 1, 2, 3, wherein the first portion 1 has a cylindrical shape complementary to the third portion 3, whereby the first portion 1 can be received fully in a third portion 3 of a further plug element 10 (see FIG. 2).

The first portion 1 has a cylindrical shape, wherein a first electrically conductive layer L1 forms a first conductor L1, and a dielectric layer D1 arranged coaxially therewith. The third portion 3 is in turn also composed from a plurality of layers arranged coaxially with one another, wherein a dielectric layer D3 is followed by a second electrically conductive layer L3, which forms a second conductor. The layer L3 forming the second conductor borders a sheathing layer U, which externally insulates the third and second portion 3, 2 over the entire periphery of the plug element 10.

The dielectric layer D1 of the first portion 1 and also the dielectric layer D3 of the third portion of a further plug element 10, when two plug elements 10 are plugged together, form the dielectric layer D (:=D1+D3) of a cylinder capacitor C, of which the structure comprises a first electrically conductive layer L1 of a first conductor, a common dielectric layer D1+D3 and also a second electrically conductive layer L3 of a second conductor.

The middle portion of the plug element 10 is formed by the portion 2. The second portion 2 connects the first portion 1 to the third portion 3 and is formed in such a way that its layer structure D2, L2, D2, U enables a homogenous layer transition when a plurality of plug elements 10 are plugged together to form a plug system 100, such that a single cylindrical capacitor C is formed, with layers of the same material and the same thickness.

By means of the plug element 10, cylinder capacitors can therefore be constructed or plugged together, of which the cylinder height corresponds to the length of the first portion of a first plug element 10 and the second portion 2 of a further plug element 10.

In a particularly preferred embodiment of the invention, the three line portions L1, L2 and L3 simultaneously form a line structure of an inductor, wherein the structure of the plug system 100 corresponds in portions to a structure of a coaxial conductor.

In FIG. 2 a plugged together structure of a plurality of plug elements 10 to form a plug system 100 is shown in a sectional view parallel to the common axis of rotation. Here, a plug system 100 comprising four plug elements 10 is plugged together to form a series connection of three cylinder capacitors C.

In a preferred embodiment of the invention, the coaxial structure of the capacitor C has an outer diameter between 10 to 50 cm with a preferably ceramic dielectric D, for example AL203 with layer thicknesses 10-50 μm, wherein a pipe wall thickness of the electric layers or conductors L1, L3 is 5 to 20 mm. This results in high capacitance values in the range of 0.5 to 10 μF/m.

Due to the high capacitances, short resonance lengths between 0.5 to 2 mm are produced. The series resonance frequency from the inductance of a short 0.5 to 2 m portion of a forward or return conductor of the induction loop and of the upper cylinder capacitors C leads to a desired resonance frequency in the range of 10 to 200 kHz. This is associated with a comparatively low inductive voltage drop between 100 and 300 volts. This voltage has to be withstood both by the dielectric D (:=D1+D3) of the cylinder capacitor and by the external insulation or sheathing U with respect to the surrounding earth. In particular, AL2O3 has a necessary high electric breakdown field strength of 20 to 30 KV per millimeter, however special glass films can also be suitable as dielectric D.

Here, the cylindrical structure of inner and outer electrode or of the electrically conductive layers L1 of the first portion and L3 of the third portion with the connecting portion 2 produce the capacitor C, which a coaxial portion that corresponds to the line structure.

FIG. 3 illustrates a further advantageous embodiment of the plug element 10 in a perspective sectional view parallel to the axis of rotation. In this embodiment of the plug element 10, the second portion 2 has radial bores B. These radial bores B enable a fluid passage, wherein fluid is transported from the reservoir into the interior of a through-opening R, here a pipe interior, in particular for conveying oil and bitumen, or from the pipe interior R into the reservoir, for example gas, water and/or salt water injection. Gas or liquid transport in the pipe interior R can also be used to cool the inductor.

FIG. 4, on the basis of a section parallel to the axis of rotation, shows a structure of a plug element 10 in accordance with a further embodiment of the invention. Here, the middle second portion 2 has grooves N arranged toward the pipe interior R.

Due to the grooves N, the rigidity of the individual plug element 10 or of the entire plug system 100 are influenced, whereby bends, for example with bend radii of 150 m, can be negotiated along drilling curves. At the same time, the mechanical voltages of the dielectric in the capacitor portion are reduced. In addition, however, the desired electric dielectric strength is maintained. In a further particularly preferred embodiment, the grooves N are filled with soft plastic. Here, soft plastic does not hinder bending, but leads to smooth inner and outer surfaces, which is advantageous when drawing in the inductor or in the case of fluid transport through the inductor (not shown here).

It is to be expected that, when plugging together individual plug elements 10, due to surface roughness and/or manufacturing tolerances, small (to tiny) air-filled gaps remain between the electrically conductive layers L1 and L3, in which gaps partial discharges could occur. Due to a special coating or covering, the cavities on the surface of the dielectric D1, D3, D can be avoided. An intermediate electrode (not shown here) is produced, with which air inclusions have no negative consequences. An ideal situation is one in which the overall layer thickness of the dielectric D (:=D1+D3) is composed from the two layers of the electrodes and is fully smooth, such that no air inclusions are created. To this end, a coating with graphite could additionally serve as a sliding layer when the plug elements 10 of the plug system 100 are plugged together.

A sheathing U made of plastic, for example PE, PVC, of the plug element 10 or plug system 100 serves as mechanical protection during installation, but does not have to meet any electrical requirements and can degrade during operation.

Further key advantages of an arrangement by means of the plug system 100 are that the inductor continues to remain operational, even in the case of short circuit of individual capacitors C, with minimally reduced resonance frequency. Furthermore, due to excellent adhesion, ceramic and high-strength Al203 layers, applied for example by PEO (plasma electrolytic oxidation) or MAO (micro-arc oxidation), enable bending at least with large radii, as are present in specified cases with oil and bitumen conveyance. 

1. A plug element (10), in particular for producing capacitors (C), which in the direction of longitudinal extent thereof comprises three portions (1, 2, 3), wherein a first portion (1) at one end of the plug element (10) has a tapered shape, which is complementary to a shape of a third portion (3) at the end of the plug element (10) remote from the first portion (1), and wherein a second portion (2) is arranged between the first and the third portion (1, 3), which interconnects the first and the third portion (1, 3).
 2. The plug element (10) as claimed in claim 1, characterized in that the plug element (10) in the direction of longitudinal extent thereof has a through-opening (R) from the end of the first portion (1) to the end of the third portion (3) remote therefrom.
 3. The plug element (10) as claimed in claim 1 or 2, characterized in that the plug element (10) is rotationally symmetrical.
 4. The plug element (10) as claimed in one of claims 1 to 3, characterized in that the individual portions (1, 2, 3) of the plug element (10) have a plurality of layers (L1, L2, L3, D1, D2, D3, U) of different material type arranged coaxially with one another, which differ in portions in terms of number.
 5. The plug element (10) as claimed in one of claims 1 to 4, characterized in that radial bores (B) can be provided in the second portion (2) of the plug element (10).
 6. The plug element (10) as claimed in one of claims 1 to 5, characterized in that radial grooves (N) can be provided in the second portion (2) of the plug element (10) and can be filled with a plastic.
 7. A plug system (100) comprising a plurality of plug elements (10) as claimed in one of claims 1 to 6, characterized in that at least two plug elements (10) can be plugged together to form a plug system (100), in that in each case a first portion (1) of a plug element 910) can be plugged into a third portion (3) of a further plug element (10).
 8. The plug system (100) as claimed in claim 7, characterized in that the coaxially arranged layers (L1, D1) of the first portion (1) of a first plug element (10) and the coaxially arranged layers (D3, L3, U) of the third portion (3) of a second adjacent plug element supplement one another to form a coaxial layer sequence, which form a cylinder capacitor C.
 9. The plug system (100) as claimed in claim 7 or 8, characterized in that a plurality of plug elements (10) can be plugged together to form a series connection of capacitors (C), wherein the individual layers (L1, D1, D3, L3, U), arranged coaxially with one another in portions, of the plug system (100) formed by means of the plug elements (10) form capacitors that are electrically connected in series via the layers (L1, L2, L3) of electrically conductive material.
 10. The plug system (100) as claimed in claim 9, characterized in that a plurality of plug elements (10), which can be plugged together to form a series circuit of a capacitors (C), simultaneously form a line structure of an inductor. 